THE UNIVERSITY OF SYDNEY Copyright and use of this thesis This thesis must be used in accordance with the provisions of the Copyright Act 1968. Reproduction of material protected by copyright may be an infringement of copyright and copyright owners may be entitled to take legal action against persons who infringe their copyright. Section 51 (2) of the Copyright Act permits an authorized officer of a university library or archives to provide a copy (by communication or otherwise) of an unpublished thesis kept in the library or archives, to a person who satisfies the authorized officer that he or she requires the reproduction for the purposes of research or study. The Copyright Act grants the creator of a work a number of moral rights, specifically the right of attribution, the right against false attribution and the right of integrity. You may infringe the author’s moral rights if you: - fail to acknowledge the author of this thesis if you quote sections from the work - attribute this thesis to another author -subject this thesis to derogatory treatment which may prejudice the author’s reputation For further information contact the University’s Copyright Service. sydney.edu.au/copyright A STRUCTURAL ANALYSIS OF THE SOUTHERN HORNSBY PLATEAU, SYDNEY BASIN, NEW SOUTH WALES by Anthony Richard Norman, B.Sc. (Hons) A thesis submitted in fulfilment of the requirements for the degree of Master of Science DEPARTMENT OF GEOLOGY AND GEOPHYSICS UNIVERSITY OF SYDNEY September, 1986 ABSTRACT The Hornsby Plateau rises north of Sydney. Aerial photo interpretation of an area north of Hornsby and south of the Hawkesbury River revealed two well defined extensive traces. These are the ESE trending Berowra Waters Fracture Lineament and the NNE trending West Head Fracture Lineament. A broad series of parallel NNE trending traces also formed the less well defined Coastal Fracture Lineament Zone. Outcrop fracture analyses revealed that these lineaments consist of master joints and conjugate fractures subparallel to the traces and that multiple deformation has taken place along the lineaments. Throughout the Hornsby Plateau outcrop examination revealed that NNE planar joints form the most widespread and dominant joint set. Some of these joints may have formed early in the history of the Sydney Basin along with N-NNE trending depositional hinge-lines. The orientation and location of these hinge lines was probably determined by structures in the basement. However, most NNE joints and joint zones appear to have formed as a result of unloading through erosion together with a residual NNE-N horizontal compression. This compression was subsequent to the intrusion of the Barrenjoey dyke about 171Ma and many NW trending dykes in the Sydney region. This NNE-N compression may be related to the present northward migration of Australia and may have commenced when separation of the Antarctic and Australian continents began about 50-60Ma. On the Blue Mountains Plateau NNW planar joints form the dominant and most widespread joint set. These joints appear to be similar in style to the NNE joints on the Hornsby Plateau and are probably related to the same residual tectonic stress and the removal of the overburden. The change in orientation of these joints across the central Sydney Basin may be related to the change in dip direction of the Permo- Triassic rocks. WNW to NW trending joints are also common on the Hornsby Plateau and are generally associated with subparallel dykes. The NW trending dykes appear to have formed an anisotropy prior to the regional NNE-N compression. The initial development of NW planar joints and joint zones may have resulted from a NE-SW extension which existed in the adjoining continental crust when the Tasman Sea rifting began to wane or ceased about 60Ma. Down-dragging of the Hornsby Plateau and Cumberland Basin from the Blue Mountains Plateau may have occurred during this period of extension and increased the rate of erosion. Prior to the NE-SW extension, rifting in the Tasman Sea may have imposed a NE compression on the south-eastern coastline. This resulted in thrusting from the NE and epeirogenic uplift and tilting. NNE trending hinge-lines were probably reactivated during this compression and deformation may have occurred within pre-existing ESE trending structures. Deformation within ESE trending structures, such as the Berowra Waters Fracture Lineament, probably initially occurred prior to the NE compression, NE-SW extension and NNE compression. This Lineament has had a complex history of deformation but may have developed initially during an E-W compression which existed after Late Permian time and is probably related to movements in the basement. ACKNOWLEDGMENTS Three years of research on the Hornsby Plateau and many years wandering through the Northern Blue Mountains would not have been possible without the help and interest of many people. I am extremely grateful to Assoc. Prof. D. F. Branagan .whose constant help and encouragement went well beyond the normal expectations of a supervisor. Many of the conceptual problems and the resulting enlightenment in structural geology came about after long discussions with Assoc. Prof. D. F. Branagan and John Creasey (C.S.I.R.O.). Much of the field work and interpretations in the Kuring-gai/Berowra were undertaken with John Creasey whose knowledge and experience were invaluable. I would like to thank the University of Sydney and C.S.I.R.O for their financial assistance with a research grant and Prof. G. M. Philip for his backing of the collaborative research fund. I am also indebted to Prof. G .M. Philip for the use of Departmental facilities and to the staff of the Department of Geology and Geophysics. For her tolerance, I want to thank Mrs. G Branagan. For help in preparing this thesis and encouragement over the last few years I owe much to my family. Their continuous support and patience were tremendous. CONTENTS INTRODUCTION Purpose 1 Outline 1 Methodology 2 1.31. The Kuring-gai/Berowra area 2 1.32. The Sydney Region 4 1.33. The Western Coalfield (southern portion) 5 1.34. The Western Margin of the Sydney Basin 6 1.35. The Lapstone Structural Complex 6 Outcrop Fracture Analysis Techniques and Terminology 7 Previous Work 9 1.51. The Hornsby Plateau 9 1.52. The Blue Mountains Plateau 18 THE KURING-GAI/BEROWRA AREA Location and access 25 Geological setting 25 Aerial-photo interpretation 28 Site Investigations 32 2.41 WNW trending structures 34 A. The Berowra Waters Lineament 34 B. St. Michael's Cave 38 2.42 NNE trending structures 39 A. The Coastal Lineament 39 B. Bobbin Head Road Structure 44 C. West Head Lineament 52 2.43 ENE and E-W trending structures 57 A. The Cowan Fracture Zone 57 B. West Head dykes 64 C. Barrenjoey Head 65 2.44 NW trending joints, faults and dykes 68 2.45 NE trending joints 71 A. The Coastal Domain 71 Interpretations 75 THE SYDNEY REGION Location and access 83 Geological setting 83 Site Investigations 87 3.31 Regional Pattern 88 A. St. Peters Brickpit 88 B. The Northern Suburbs Railway I05 C. The Coastal Region I07 3.32 NNE trending structures 115 A. The West Head Lineament 115 B. Pyrmont-Lavender Bay-North Sydney-Anderson 118 Park Fracture Zones C. Art Gallery-Mrs Macquarie's Chair-Cremorne- 125 Balmoral Fracture Zone 3.33 ENE to ESE trending joints and faults 134 3.34 NNW trending structures 136 A. The Roseville Warp 136 B. The Hornsby Warp 140 3.35 NW and NNW trending joints, faults and dykes 142 3.4 Interpretations 150 Chapter 4 THE BLUE MOUNTAINS PLATEAU 161 4.1 The Lapstone Structural Complex 162 4.2 The Western Coalfield (southern portion) 168 A. Regional geology of the Northern Blue 169 Mountains B. Regional structure of the Western 173 Coalfield (southern portion) 4.3 Basement Structures 180 A. Kanangra Walls region 180 B. Coco Creek unconformity 184 4.4 Summary 188 Chapter 5 STRUCTURAL SYNTHESIS AND COMPARISON BETWEEN THE HORNSBY PLATEAU AND BLUE MOUNTAINS PLATEAU 193 REFERENCES 212 APPENDICES Appendix A - Fracture analysis summaries of 59 A1-A34 localities in the Kuring-gai/Berowra area. Appendix B - Fracture analysis summaries of 65 B1-B36 localities in the Sydney region. Appendix C - Fracture analysis summaries of 11 C1-C7 localities on the Blue Mountains Plateau. FIGURES page Figure 1. Location of the study areas and the structural 3 subdivisions of the Sydney Basin (Bembrick et al., 1973). Figure 2. The main structural features of the southern 10 Hornsby Plateau, Cumberland Basin and Woronora Plateau (Branagan, 1985). Figure 3. Rose diagram of dyke, lineament and fault 13 orientations in the Sydney City area from reports by the Snowy Mountains Hydro-electric Authority (1968, 1969a, 1969b). Figure 4. Contoured equal area polar plot of joints and 13 joint zones intersected during tunnelling for the eastern suburbs railway. Figure 5. Structural synthesis of the Sydney 16 1:100,000 sheet (Mauger et al., 1984). Figure 6. Structural synthesis of the Katoomba, Wallerawang 22 and Mt. Pomany 1:100,000 sheets (Mauger et al., 1984) Figure 7. Location of the Kuring-gai/Berowra study area. 26 Figure 8. Airphoto lineament interpretation map of the (in back pocket) Kuring-gai/Berowra area. Figure 9. Rose diagram of photo linear azimuths. 31 Figure 10. Lineament summary of Kuring-gai/Berowra area. 31 Figure 1 1. Outcrop fracture analysis sites in the 33 Kuring-gai/Berowra area. Figure 12. Fracture analysis map of the Kuring-gai (in back pocket) /Berowra area. Figure 13. Equal area polar plot and rose diagram of 35 fracturing along Berowra Waters Lineament. Figure 14. A zone of intense fracturing within the 37 Berowra Waters Lineament (Locality 6).